A ways back I was able to do this by making a copy of all my maps into a folder named original_maps and then in the game folder then rename the map that starts at launch to a name that isnt already in use such as default_oldmap, then rename the map you want as the default map name for the on game launch's map name.
BUT this only works if the map doesnt work in pairs with other files. That is you could rename the map you want to the default at launch map name and this will load that map, but the handlers for that map may be incorrect based on how the program itself runs with the map. You might have a situation where you have level 8 map and level 1 handlers in which the game crashes.
If you run into problems with this, simply delete the maps that were altered, and copy the clean unedited copies of these over from the original_maps folder back to the game directory that they are required in.
